1. Field of the Invention
Semiconductor manufacturing is a highly competitive industry. Success requires the ability to produce high quality, high reliability semiconductor devices at low cost. That requires an ability to rapidly fabricate complex devices at high speed and with high yields.
2. Discussion of the Related Art
Semiconductor manufacturing is a highly competitive industry. Success requires the ability to produce high quality, high reliability semiconductor devices at low cost. That requires an ability to rapidly fabricate complex devices at high speed and with high yields.
The fabrication of a semiconductor device begins with a semiconductor wafer. Such wafers are made by carefully growing a large semiconductor crystal, and then slicing that crystal into individual wafers. For storage and protection the sliced wafers are usually loaded into wafer cassettes. A wafer cassette individually stacks sliced semiconductor wafers in slots. Wafer cassettes are beneficial in that the large numbers of semiconductor wafers can be stored and transported in a protected environment.
Unfortunately, immediately after slicing a semiconductor wafer is unsuitable for fabricating semiconductor devices because the cutting leaves rough surfaces. Surface roughness is a problem because modern fabrication processes require accurate focusing of photolithographic circuit patterns of the semiconductor wafer. As the density of integrated circuits increases, focus tolerances better than 0.1 xe2x96xa1meters can be required. Focusing with such small tolerances is not practical if the surface of a semiconductor wafer not highly planar.
A number of techniques for reducing surface roughness exist. In practice, a semiconductor wafer can be mechanically worked by an abrasive pad to produce a fairly smooth surface. However, as indicated above, the surface of a semiconductor wafer needs to be rendered exceptionally smooth.
One technique that can finish the surface of a semiconductor wafer to the required smoothness is Chemical-Mechanical Polishing (xe2x80x9cCMPxe2x80x9d). In CMP, a semiconductor wafer is mechanically and chemically worked under carefully controlled conditions. Such work is performed using a special abrasive substance that is rubbed over the surface of the semiconductor wafer. The special abrasive substance is typically slurry containing minute particles that abrade, and chemicals that etch, dissolve, and/or oxidize the surface of the wafer.
The mechanical work is performed by polishing pads. By inducing relative motion between a polishing pad and a semiconductor wafer, and by using the abrasive substance, the surface of the semiconductor wafer is planarized.
In addition to mechanically and chemically working a semiconductor wafer, a complete CMP process requires careful cleaning and drying of the semiconductor wafer, and testing to ensure the smoothness and electrical characteristics of the semiconductor wafer. Cleaning and drying is beneficially performed without contaminating the semiconductor wafer. Testing is typically performed using a metrology station. Thus, a functional CMP process requires removing semiconductor wafers from a wafer cassette, CMP polishing, cleaning, drying, testing, and then storing completed semiconductor wafers in a wafer cassette.
Obviously, each of the foregoing process functions involve moving semiconductor wafers from one processing station to the next. To reduced cost, and to avoid damage and contamination, such movement is beneficially performed robotically.
Therefore, a complete CMP process includes a Chemical-Mechanical Polishing system, a cleaning system (which beneficially includes a metrology station), and motion inducing devices that move semiconductors wafers from a starting station, through the CMP process, and to an ending station.
There are many well-known stations that can be used to implement a CMP process. For example, FIG. 1 schematically illustrates a conventional Chemical-Mechanical Polishing system in the form of a mini-polisher 10. That polisher includes a large pad 14 on the end of a rotated shaft 16. A semiconductor wafer 20 is located on the large pad 14. A small amount of a special abrasive substance 23 is placed over the surface of the semiconductor wafer 20. Then, a small pad 30 on the end 32 of a rotating small shaft 36 is brought into contact with the surface of the semiconductor wafer 20. Rotation-induced mechanical abrasion, combined with chemical action, polish the semiconductor wafer. Such CMP systems are well known, reference U.S. Pat. Nos. 5,542,874; 5,944,582; and 6,106,369, all of which are hereby incorporated by reference.
While mini-polishers can produce high quality planar surfaces on semiconductor wafers, a mini-polisher requires a relatively long polishing time when compared to polishers that use large pads. However, U.S. Pat. Nos. 6,169,693 and 6,062,594 disclose polishing systems that use multiple polishing stations.
In particular, U.S. Pat. No. 6,062,594 discloses a system having three mini-polishers. A semiconductor wafer is polished at a first station, then by the second, and finally by the third. Such serial polishing can dramatically increase throughput. However, serially moving a semiconductor wafer from one station to the next might not be optimal. Furthermore, the internal mechanisms of transferring the semiconductor wafers also might not be optimal.
In any event, a typical cleaning system for polished semiconductor wafers includes three cleaning stations. In the first and second cleaning stations, the slurry particles are removed by mechanical contact with brushes. In the first cleaning station NH40H containing de-ionized water can be used to remove particles. In the second cleaning station, a dilute HF solution can be used to lightly etch the semiconductor wafer""s surface while removing contaminates and slurry. In the third cleaning station, the semiconductor wafer is rinsed with de-ionized water and dried. While three cleaning stations are typical, the actual number and composition of cleaning stations can vary. But, 2, 3, or 4 stations are the most common.
As semiconductor manufacturing is highly competitive, it is desirable to maximize the rate of polishing semiconductor wafers, while simultaneously minimizing the number of defects. To reduce cost, an automated CMP process is beneficially. Furthermore, as CMP processes tend to be expensive, it is highly desirable to efficiently utilize the systems that comprise the CMP process. Thus, it is desirable to maximize the number of finished semiconductor wafers per hour.
Furthermore, as CMP is typically performed in a clean room, and as clean rooms are expensive, and as that expense tends to increase with the size of the clean room, it is very desirable to minimize the size of the clean room. Minimizing the clean room size requires efficient space utilization. Thus, a CMP system ideally should have a small footprint. In order to achieve a small footprint, the CMP polisher system, the cleaner system, and the input/output and motion inducing systems should be considered together.
In view of the foregoing, it is obvious that a new, integrated CMP system that implements the CMP process would be beneficial. Even more beneficial would be a new, integrated and automated CMP system. More beneficial yet would be a new, automated integrated CMP system having a reduced footprint. Still more beneficial would be a new, automated integrated CMP system that enables a small footprint and that has a high throughput.
Accordingly, the principles of the present invention provide for a new, integrated CMP process. Those principles further provide for a new, automated integrated CMP process that can be implemented with a small footprint and with a high throughput.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a semiconductor wafer processing system according to the principles of the present invention includes a wafer load station for receiving semiconductor wafers stored in a first wafer load cassette, at least one CMP polishing system for polishing the semiconductor wafers, and at least one multi-station cleaning system for cleaning the polished semiconductor wafers. Also included is at least one unload station for receiving polished and cleaned semiconductors and a robotic system. In some applications there are multiple CMP polishing systems, multi-station cleaning systems, and/or multiple unload stations. In some applications, multiple CMP polishing systems are vertically stacked. In some applications the wafer load and wafer unload stations are capable of vertical motion. In some applications the wafer load station is track mounted. In some applications a multi-station cleaning system includes a metrology station. In some applications a multi-station cleaning system is vertically stacked. Some applications have a buffer station, which can include vertically stacked buffer plates. In some applications the buffer station is capable of vertical motion.
The robotic system includes a first robotic mover. In some applications the first robotic mover moves semiconductor wafers from the wafer load station into the CMP polishing system. In some applications the first robotic mover moves semiconductor wafers from the wafer load station into a buffer station, which can include a plurality of vertically stacked buffer plates. In some applications the first robotic mover moves semiconductor wafers from the CMP polishing system into the multi-station cleaning system. In some applications the first robotic mover moves semiconductor wafers from the CMP polishing system into the buffer station. In some applications the first robotic mover moves semiconductor wafers from a station of the CMP polishing system into another station of the CMP polishing system. In some applications the first robotic mover is track mounted. In some applications, the first robotic mover is capable of Z-axis motion. In some applications the first robotic mover moves semiconductor wafers from the multi-station cleaning system to an unload station.
The robotic system also includes a second robotic mover. In some applications, the second robotic mover moves polished semiconductor wafers from a buffer station into the multi-station cleaning system. In some applications the second robotic mover moves semiconductor wafers from a buffer station to a CMP polishing system. In some applications the second robotic mover moves semiconductor wafers from a CMP polishing system to a buffer station. In some applications the second robotic mover is capable of Z-axis motion.
The robotic system can also includes a third robotic mover. In some applications, the third robotic mover moves polished semiconductor wafers from a buffer station into a multi-station cleaning system. In some applications the third robotic mover moves semiconductor wafers from a CMP polishing system to a multi-station cleaning system. In some applications the third robotic mover moves semiconductor wafers from a multi-station cleaning system to a wafer unload station. In some applications the third robotic mover is capable of Z-axis motion.
The robotic system can also includes a fourth robotic mover. In some applications, the fourth robotic mover moves polished semiconductor wafers from a buffer station into a multi-station cleaning system. In some applications the fourth robotic mover moves semiconductor wafers from a CMP polishing system to a multi-station cleaning system. In some applications the fourth robotic mover moves semiconductor wafers from a multi-station cleaning system to a wafer unload station. In some applications the fourth robotic mover is capable of Z-axis motion.
The robotic system can also includes a fifth robotic mover for moving polished and cleaned semiconductor wafers from a multi-station cleaning system into a wafer unload station. In some applications the fifth robotic mover is on a track.
The robotic system can also includes a sixth robotic mover for moving polished and cleaned semiconductor wafers from a multi-station cleaning system into a wafer unload station.
A method of polishing semiconductor wafers according to the principles of the present invention includes receiving a semiconductor wafer having a surface area at a load station. Then, transferring the received semiconductor wafer from the load station to a polishing station. The method further includes polishing the received semiconductor wafer using a polishing pad and a chemical slurry, wherein the polishing pad contacts less than the first surface area. Then, transferring the polished semiconductor wafer from the polishing station to a cleaning station. At the cleaning station the polished semiconductor wafer is cleaned, rinsed, and dried. Finally, transferring the dried semiconductor wafer from the cleaning station to an unload station. In some applications the semiconductor wafers will be moved vertically, and/or semiconductor parameter measurements will be taken of the semiconductor wafers.
Another method of polishing semiconductor wafers according to the principles of the present invention includes receiving semiconductor wafers, each having a surface area, at a wafer load station. Then, selectively transferring the semiconductor wafers from the wafer load station to a first CMP polishing station or to a second CMP polishing station. Then, polishing the semiconductor wafers in the first or second CMP polishing stations using a polishing pad and a chemical slurry, wherein the polishing pad contacts less than the surface area. Then, transferring the polished semiconductors from the first or second CMP polishing station to a first or second cleaning station. Then, cleaning the polished semiconductor wafers and unloading them to a first or second unload station. In some applications the semiconductor wafers will be moved vertically, and/or semiconductor parameter measurements will be taken of the semiconductor wafers.
Another method of polishing semiconductor wafers according to the principles of the present invention includes receiving semiconductor wafers, each having a surface area, at a wafer load station, and then transferring the received semiconductor wafers from the wafer load station to a buffer station that temporarily retains the semiconductor wafers. Then, selectively transferring semiconductor wafers from the buffer station to a first CMP polishing station or to a second CMP polishing station. Then, polishing the semiconductor wafers in the first or second CMP polishing stations using a polishing pad and a chemical slurry, wherein the polishing pad contacts less than the surface area. Then, transferring the polished semiconductors from the first or second CMP polishing station to a first or second cleaning station. Then, cleaning the polished semiconductor wafers and unloading them to a first or second unload station. In some applications the semiconductor wafers will be moved vertically, and/or semiconductor parameter measurements will be taken of the semiconductor wafers.
Yet another method of polishing semiconductor wafers according to the principles of the present invention includes receiving semiconductor wafers, each having a surface area, at a wafer load station,, and then transferring the received semiconductor wafers from the wafer load station to a buffer station that temporarily retains the semiconductor wafers. Then, selectively transferring semiconductor wafers from the buffer station to a first CMP polishing station or to a second CMP polishing station. Then, polishing the semiconductor wafers in the first or second CMP polishing stations using a polishing pad and a chemical slurry, wherein the polishing pad contacts less than the surface area. Then, transferring the polished semiconductor wafers from the first or second CMP polishing stations to the buffer station for temporary storage. Then, selectively transferring semiconductor wafers from the buffer station to a first cleaning station or to a second cleaning station. Then, cleaning the polished semiconductor wafers and then unloading the cleaned and polished semiconductor wafers to a first unload station or to a second unload station.
Still another method of polishing semiconductor wafers according to the principles of the present invention includes receiving semiconductor wafers, each having a surface area, at a wafer load station, and then transferring the received semiconductor wafers from the wafer load station to a buffer station that temporarily retains the semiconductor wafers. Then, selectively transferring semiconductor wafers from the buffer station to a CMP polishing station. Then, polishing the semiconductor wafers in the CMP polishing station using a polishing pad and a chemical slurry, wherein the polishing pad contacts less than the surface area. Then, transferring the polished semiconductor wafers from the CMP polishing station to a cleaning station. Then, cleaning polished semiconductor wafers at the cleaning station; and unloading the polished and cleaned semiconductor wafers station to an unload station.
Additional features and advantages of the invention will be set forth in the description that follows, will be apparent from the description and/or the figures, or may be learned by practice of the invention.